This study aims to test the acute and subchronic effects of nicotine in relieving some of the cognitive symptoms of Alzheimer's disease and cognitive and motor symptoms of Parkinson's disease. Each subject receives three doses of nicotine, placebo, plus highest tolerated dose of nicotine+mecamylamine. On each treatment day cognitive testing includes measures of attention, learning and memory, motor speed, and cognitive strategies. After this intravenous study phase, subjects were placed on a nicotine transdermal patch for up to three weeks, and tested again.